Magnetic ion exchange resins have been used to remove various compounds from water supplies and waste streams. The resins are used to remove and concentrate a compound or compounds from a stream and move the compound into another stream. The term “compound” includes chemical compounds, elements and ions.
Ion exchange resins work by having functional groups incorporated within a polymer backbone which bind to compounds present within a solution to be treated. The functional groups can be selected so to provide binding sites suitable for binding to various types of compounds present within a solution. Weak acid cationic ion exchange resins are suitable for separating transition metal ions. Acidic organic materials, such as DOC and other negatively charged ions, will bind to anion ion exchange resins. The binding effectiveness of the resin decreases as the compounds use up available binding sites of the resin. The spent resin is regenerated by applying a regenerate wash solution to the resin to reform the binding sites. Treatment with a regenerant solution produces a wash solution containing the separated compounds.
For ease of handling traditional ion exchange resins are contained within columns and the solution to be treated is pumped through the column. This restricts the types of processes in which the resin can be used.
Magnetic ion exchange resins are a significant improvement over traditional ion exchange resins. These resins have a discrete magnetic core or have magnetic particles dispersed throughout the resin. MIEX® brand resin from Orica Australia Pty Ltd is a magnetic ion exchange resin having magnetic particles dispersed throughout the resin and is particularly suitable for use in removing dissolved organic carbon (DOC) from potable water supplies. It has an advantage over other types of magnetic resins as all parts of the resin contain magnetic particles.
As described in U.S. Pat. No. 6,669,849 magnetic ion exchange resins can be used in the treatment of potable water supplies to remove dissolved organic compounds and are referred to as dissolved organic carbon (DOC). It can be used as part of a multi-step treatment process and can provide a number of benefits in addition to the direct removal of DOC. For example some water treatment processes employ activated carbon as a final polishing treatment to alleviate problems with taste and/or odour, to remove disinfection by-products or to remove any other pollutants. Pre-treatment with MIEX resin may also extend the effective life of the activated carbon.
Magnetic ion exchange resin can also be used in the treatment of waste streams. For example the Kraft process produces a highly coloured black effluent which is often released into water ways. Resin may be used to remove the colouring compounds from the effluent waste stream. Resin can also be used to remove and concentrate heavy metals from waste streams for additional processing.
A benefit of using magnetic ion exchange resins is that the weak magnetic properties of the resin allow the resin particles or beads to agglomerate together and quickly settle in settling tanks. This can facilitate the separation of resin from solution and thereby improve the methods of removing, recycling and regenerating resin. This has removed the need for columns to contain the resin and has permitted new treatment arrangements and methods for regenerating the resin, and continuous flow systems.
Processes for the use and separation of resins for use in the treatment of potable water are known and some have been described in U.S. Pat. No. 6,669,849. Magnetic ion exchange resins are described in U.S. Pat. Nos. 5,900,146 and 6,171,489. Other applications and patents relating to magnetic resins include International Application Nos. PCT/AU2005/001111, PCT/AU2005/000419, PCT/AU2004/000432, PCT/AU2005/000618, PCT/AU2005/001426 and U.S. application Ser. No. 11/124,624. The contents of these documents are incorporated by cross-reference.
There are a number of known methods for settling and separating the magnetic ion exchange resins from solution (or vice versa). Settling tanks and tube settlers are disclosed in U.S. Pat. No. 6,669,849. Such tanks take up a large amount of space and can significantly increase the capital cost of using a magnetic ion exchange resin process. The effectiveness of various existing systems can significantly decrease at higher solution flow rates and with smaller sized particles.
U.S. Pat. Nos. 5,397,476 and 5,855,790 (Bradtec Limited) relate to a method of removing pollutant ions by using magnetic resins. The magnetic resin particles are removed by magnetic filtration from the solution. The method of magnetic filtration is not specifically described.
U.S. Pat. No. 4,523,996 (Charles et al) relates to a differential separation process for use with mixed bed systems for the treatment of water in power plants. A bed contains a mixture of two types of resin beads, namely one type containing ferromagnetic material such as magnetite and another having different magnetic properties. The beads are separated by the use of an inhomogeneous magnetic field (e.g. by applying a permanent magnet to a part of a containment vessel).
U.S. Pat. No. 5,230,805 (Yates et al) relate to magnetically stabilised fluidised particles in liquid media. Fluidised magnetic resins in an upwardly flowing liquid stream are stabilised within a general area by the application of a magnetic field of 25 to 500 gauss, preferably by an electromagnet that encircles the treatment bed. Such an arrangement can avoid the need to use a large settling tank downstream to recover the resin but requires an ongoing strong magnetic field to retain the resin beads with a contact region. It is unlikely that the resin could be economically retained within the region at high flow rates.
U.S. Pat. No. 5,110,624 (Noble et al) relates to a method for preparing magnetisable porous particles (resins). Like Yates above, the ion exchange resins are held within a bed subjected to a uniform magnetic field as a solution is passed upwardly through the bed.
It would be beneficial to provide a solution to the above mentioned capital and effectiveness (at high flow rates) problems associated with using settling tanks such as those used in the traditional MIEX resin process. Ideally the solution would involve equipment which is relatively simple to install, maintain and operate.
Another problem with the use of ion exchange resins in mobile resin systems relates to the damage done to the resin and the associated formation of resin fines and larger particles and fragments or portions of resin beads. These fines, portions and particles may be the product of physical interactions between resin beads themselves or resin beads and the surfaces in contactor, settler or regeneration vessels, mixing blades, pumps or other equipment used in the treatment plant. The interactions damage individual resin beads and produce smaller fragments. Systems designed for separating and recycling the larger resin beads from the treated fluids may not effectively work for the removal of the smaller resin fines, portions or particles.
A solution to this problem is the use of a bed of particulate magnetite such as that described in the co-pending PCT application entitled “Water Polishing Process” by the same applicant filed on 15 Dec. 2005. However, it would also be advantageous if the settler system also removed any resin fines or other particulate matter in the fluid streams.